1. Field of the Invention
The present invention is directed to enzyme assisted degradation of surface membranes of unmacerated harvested fruits and vegetables. In particular, the present invention utilizes degradation enzymes such as cutinases, lipases, cellulases, pectinases, etc., to degrade one or more of the water insoluble components which comprise part of the surface membrane of the fruits and vegetables. Preferably, the surface of the fruit or vegetable is sufficiently degraded so as to result in an increase in water permeability across the surface membrane of at least 50 percent as compared to untreated surfaces. The increased water permeability across the surface membrane permits more facile delivery of substances such as flavorings, sweeteners, stabilizers, and preservatives to the interior of the fruit or vegetable. Additionally, the increased water permeability allows for the more efficient dehydration of fruits and vegetables.
2. Related Art
The surface membranes of fruits and vegetables contain one or more types of water insoluble components which significantly limit the permeability of water across the membrane. Accordingly, this membrane serves the useful role of preventing the evaporation of liquids contained in fruits and vegetables both prior to and after the harvesting of such fruits and vegetables. On the other hand, the production of dried fruits and vegetables at temperatures of from about 10.degree. C. to about 50.degree. C. require the evaporation (dehydration) of water from the interior of harvested fruits or vegetables. Harvested fruits and vegetables are dried for a variety of reasons. First and most important, dehydration is a method of fruit preservation. Additionally, certain dried fruits and vegetables, i.e., raisins, prunes, apricots, sun-dried tomatoes, etc., have desirable properties not present prior to drying. One means commercially utilized for drying fruits and vegetables is by osmosis. However, as noted above, the water insoluble components contained in the surface membranes of fruits and vegetables render the surface not completely permeable to water. Thus, while the membranes of cells of fruits and vegetables (below the surface membrane) are selectively permeable to molecules such as water and are therefore susceptible to osmosis, the surface membranes of harvested fruits and vegetables limit osmosis as a means for effecting dehydration. In particular, such osmotic processes inherently require prolonged dehydration.
Additionally, the lack of significant water permeability across this membrane also interferes with the osmotic transport of either natural or synthetic substances into the interior of the fruit or vegetable. On the other hand, the delivery of substances, such as sweeteners, flavor enhancers, preservatives, stabilizers, etc., into the interior of such products could provide beneficial results.
Certain chemicals such as organic solvents, including methanol, chloromethanes (chloroform, methylene chloride), etc., alkali metal hydroxides, etc., can be used to enhance the water permeability of the surface membrane. However, the use of such chemicals is not desirable because traces of these chemicals are retained in the final product and the subsequent ingestion of these chemicals could pose potential harmful side effects. Worker exposure to these chemicals is undesirable and waste treatment of these chemicals is hazardous and difficult. Furthermore, a growing concern among consumers regarding chemicals in food products makes these products less desirable.
While numerous degradation enzymes are known in the art with some being commercially available, these degradation enzymes are primarily known for their role in fruit and/or vegetable decay. On the other hand, some references disclose the use of enzymes on fruit and/or vegetables for the purpose of providing enhanced protection for the treated product.
For example, European Patent Application Publication No. 302 685A discloses the use of an auxin destroying material on the surface of fruit which reduces the occurrence of russeting on the fruit. Auxin is defined by this reference as chemicals, i.e., indole-3-acetic acid, etc., having common biological properties in plants such as stimulation of cell division, stimulation of shoot growth, control of vascular system differentation, control of tissue culture differentation, control of apical dominance, etc. The auxin destroying materials include microorganisms or compositions containing purified components thereof which can destroy the auxin by chemical degradation. Presumably, the auxin destroying material generated by these microorganisms is an enzyme.
Likewise, U.S. Pat. No. 4,762,547 as well as U.S. Ser. No. 297,224 filed Jan. 13, 1989 abandoned in favor of continuation application U.S. Ser. No. 07/411,084, filed Sep. 22, 1989 which has been abandoned in favor of continuation application U.S. Ser. No. 07/663,055, filed Mar. 1, 1991 discloses the use of esterases, i.e., degradation enzymes, in combination with a biocide. These references disclose that when the esterase is used in conjunction with a biocide, which can be applied either separately or in combination, the esterase results in enhanced biocide activity. U.S. Pat. No. 4,762,547 speculates that the esterase decomposes the foliar wax (surface membrane) of the plant or the epidermal wax of insects, thereby permitting a larger amount of the biocide to enter the treated plant or insect thus resulting in greater biocide activity. Implicit in these references is the fact that the esterase and biocide are applied to plants prior to harvesting.
However, none of these references disclose the use of esterases on the surface membranes of harvested fruits and vegetables as a means for enhancing the water permeability across this surface.
Accordingly, it is an object of this invention to enhance the water permeability of the surface membrane of harvested fruits and vegetables without the use of chemicals which could pose potential harmful side effects if ingested. Such permeability should preferably be increased by at least 50 percent as compared to untreated surfaces.
It is a further object of this invention to facilitate the dehydration of fruits and vegetables without the need for chemicals which act to enhance the surface membrane's water permeability.
It is still a further object of this invention to facilitate the delivery of desirable substances to the interior of the fruit or vegetable.
These and other objects are achieved by the present invention as evidenced by the attached summary of the invention, detailed description of the invention, examples, and claims.